Now the power supply net goes the way for high voltage and large current, and requires the increasing voltage and current of the transformer. Therefore, the tap switch matched with the transformer is required to have the ability of carrying high voltage and large current.
In the prior art, in order to increase the current-conducting capability of the contact head, two or more contact points can be arranged at one contact head end. Due to the external force and the internal stress in the process of manufacturing, it tends to make contact point(s) on the moving contact head with more contact points can't completely contact with the static contact head, so that the contacting resistance is larger, which doesn't play the role of increasing contact points and causes to heat and also shorten the lifetime of the contact points. It is now widely used, such as M type switch 1, as is shown in FIG. 1, and the front end of its contact head is equipped with two contact points 11 and 12.
Another method to increase current is that the spring is used to increase the contact pressure of the contact head. However, the pressure increase is limited, because the effect of pressure on current increase is reduced after the pressure is increased to a certain extent. On the other hand, too much pressure also has an adverse effect on the changeover between contact heads. There are movable contact heads used in such methods for increasing current, such as existing double-contact-point holder-type contact head, shown in FIG. 2. An upper contact head 21 and a lower contact head 22 of the double-contact-point holder-type contact head are holder-shaped and tightly compressed by using cylindrical helical spring 27. In order to increase the conductive capability of the upper contact head 21 and the lower contact head 22, the ends of the upper and lower contact heads 21, 22 are equipped with contact points 23, 24, 25 and 26, so that each end of the moving contact head 2 is corresponding up and down, that is, the moving contact head 2 has four contact points, but in this manner, the maximum current of the tap switch is also only 600 A.